Field of the Invention
The invention relates to a drive device for a washing machine, having a laundry drum mounted through an at least approximately horizontally disposed shaft within a bearing sleeve of a rigid carrying part attached to a bottom wall of a tub and driven directly by a flat motor likewise attached to the rear side of the tub.
Such drive devices are known from German Published, Non-Prosecuted Patent Applications DE 39 27 426 A1 and DE 43 41 832 A1 . In those devices, the stator of the motor, which is constructed as a commutatorless external-rotor direct current motor, is fastened directly to the bearing sleeve of the rigid carrying part. The shaft is mounted in the bearing sleeve and has an outer end connected fixedly in terms of rotation to the rotor of the motor. In that case, the rotor is a so-called external rotor which engages as a can over the stator windings and which carries poles constructed as permanent magnets. In the washing machine according to German Published, Non-Prosecuted Patent Application DE 43 41 832 A1, the motor is additionally surrounded by an insulating hood which damps noises radiated directly from the motor into the ambient atmosphere.
The known drive devices encase the stator, which is exposed to considerable thermal load due to Joule heat in its windings, through the use of a can-shaped rotor (and additionally through the use of the sound insulating hood in the case of German Published, Non-Prosecuted Patent Application DE 43 42 832 A1) to such an extent that cooling of the motor fails altogether. Above all, inability to cool is exacerbated by the fact that a directly driving motor of that type has difficulty in cooling itself through the use of the rotating rotor, because it necessarily has low inherent rotational speeds. The known drive devices can therefore only be used in practice when they are protected against rapid overheating through the use of separate cooling.
Moreover, the known drive devices cannot be delivered as ready-assembled motors to the factory manufacturing the washing machines. Their stators and rotors have to be delivered separately and can only be assembled together at the washing machine factory. As a rule, a washing machine factory does not have special assembly equipment available for the completion of motor subassemblies, and is also not desired. Therefore, the stator subassembly which is initially to be connected to the tub system is usually completed with the external rotor subassembly without any great accuracy. Since extremely stringent requirements are placed on maintaining a small airgap between the stator poles and rotor poles, if possible the airgap is always of equal size in each article, and the above-mentioned assembly in a washing machine factory does not satisfy those requirements on centered mounting, in practice the known drive device can only be used with great reservations.